Insert video to sequence editor with python Script
When invoking an operator in python, there are three positional arguments that are generic to all operators, all other arguments that pass settings specific to the operator must use keyword arguments.

So to call the operator you should use -

bpy.ops.sequencer.movie_strip_add(filepath=video_file)


Note that movie_strip_add will add one video file as a strip, so to add a directory of movies you will want to use a loop.

def execute(self, context):
    episode_path = "/path/to/videos/"
    for v in [f for f in os.listdir(episode_path) if f.endswith('.mov')]:
        bpy.ops.sequencer.movie_strip_add(filepath=os.path.join(episode_path,v))
    return {'FINISHED'}